This invention relates to a method of increasing the water repellency of water-wettable, bonded, non-woven fabrics bearing a surfactant.
Disposable diapers have been well accepted by consumers because they provide substantial advantages from the standpoint of convenience. Most disposable diapers incorporate three basic elements into their construction: a water impervious backing sheet, a water-permeable facing sheet, and an absorbent cellulosic batt situated between the facing sheet and the backing sheet.
One advantage which disposable diapers may have over non-disposable cloth diapers is that the multilayer disposable diaper, such as the diaper disclosed in U.S. Pat. No. 3,612,055 to Mesek et al., may be constructed so that when an infant voids into the diaper, the absorbent batt layer will absorb and retain the urine, while the facing sheet which is situated next to the infant's skin remains dry. To accomplish this result, the facing sheet must be less wettable than the absorbent batt. However, the facing sheet must be wettable, as opposed to being water repellent, since a water repellent facing sheet could undesirably impede or prevent the penetration of excreted body fluids through the facing sheet and into the absorbent layer or layers behind it.
It is commercially advantageous to construct the facing sheet from short-length cellulosic fibers, such as fibers of wood pulp or cotton linters, as is disclosed in U.S. Pat. No. 3,633,348 to Liloia et al. Facing sheets constructed in accordance with this patent are less expensive than facing sheets made from woven fabrics, and thus are better suited for use in disposable diapers.
The method of preparing the bonded, non-woven facing sheet disclosed in U.S. Pat. No. 3,633,348 to Liloia et al. includes the steps of forming a web of randomly laid dry fibers, impregnating the web with a binder and a surfactant, and drying the web to form the facing sheet. The surfactant is included in the step of impregnating the web with the binder in order to offset the water-repellency which the binder imparts to the normally cellulosic fibers. To optimize diaper performance, it would be desirable to control the wettability of the diaper facing so that some areas or regions of the diaper facing are more wettable than other areas or regions thereof.
U.S. Pat. No. 3,730,184 to Mesek discloses a method for preparing a non-woven facing sheet having a controlled degree of wettability in which the central portion of a web of randomly laid dry fibers is treated with a binder and a surfactant while the marginal portions of the web are treated with binder material alone. Facing sheets which are products of this method have marginal portions which are substantially water repellent, due to the repellency imparted to the fibers by the binder, and central portions which are substantially water absorbent. However, the degree to which the wettability of different regions of a diaper may be controlled is limited by the configuration of the apparatus for distributing the surfactant and binder-containing solutions.